Personal computers were initially connected to the telephone network by means of telephone couplers which were connected either via a telephone handset or via a modem associated with a telephone set, thereby enabling data to be transmitted in the telephone band between the computer and remote compatible computer equipment via telephone apparatus (integrated or otherwise) at said computer equipment and after a telephone call had been established by means of the telephone set to the telephone apparatus of said remote computer equipment. However, such a solution is not very satisfactory particularly insofar as the user must switch back and forth between acting on the telephone set and the on computer while setting up a call, during transmission over the telephone network, and while clearing down a call, thereby increasing the danger of making mistakes.
At present, personal computers are more commonly connected to a public or private telephone network by means of a circuit card which is connected to an extension connector (or "slot") incorporated in the computer for possible adaptations. Such a circuit card performs the telephone functions normally performed by subscriber telephone sets and by the subscribers themselves, e.g. dialing like a subscriber or detecting ringing like a telephone set.
One of the drawbacks of such an arrangement is that it monopolizes one of the extension connectors of the computer and the number of such connectors is often insufficient.
In addition, the connection between the computer and a telephone line takes place in this case either in parallel with a telephone set which is temporarily taken out of use while the computer is using the line, or else instead of a telephone set with the telephone line then being reserved for the computer only.